Mixed oxide

About: Mixed oxide is a research topic. Over the lifetime, 5224 publications have been published within this topic receiving 115567 citations.

Phase-pure Cu,Zn,Al Hydrotalcite-like Materials as Precursors for Copper rich Cu/ZnO/Al2O3 Catalysts

Abstract: A series of hydrotalcite-like (htl) compounds of the general composition (Cu,Zn)1−xAlx(OH)2(CO3)x/2·m H2O was prepared with a fixed Cu:Zn ratio of 70:30. Phase pure samples could be obtained for 0.3 ≤ x ≤ 0.4. The htl precursors thermally decompose in multiple steps. After dehydration and dehydroxylation amorphous materials were obtained at 330 °C. Phase segregation during this mild calcination was only observed for samples with a Zn:Al ratio deviating strongly from 1:2. A mechanism for this low-temperature segregation process basing on the preformation of the ZnAl2O4 phase within the amorphous material is proposed. Samples with Zn:Al ratios near 1:2 form an amorphous carbonate-modified mixed oxide “(CuO)x(ZnAl2O4)y” of homogeneous microstructure. Crystallization occurs upon carbonate decomposition at temperatures higher than 500 °C. Despite the small size of the Cu nanoparticles (around 7 nm) formed upon reduction, the accessible Cu surface area is below 5 m2g−1. This can be explained by the unfavorable ...

XPS, XANES and EXAFS investigations of CuO/ZnO/Al2O3/ZrO2 mixed oxide catalysts

Abstract: Systematic X-ray photoelectron spectroscopy (XPS), X-ray induced Auger electron spectroscopy (AES), X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) studies were undertaken to investigate the electronic structure, chemical states and local geometry of the active species in the CuO/ZnO/Al2O3/ZrO2 multicomponent mixed oxide catalysts employed in the oxidative steam reforming of methanol (OSRM) reaction for H2 production. The core level XPS and AES indicated the existence of CuO and ZnO-like species. Two kinds of zirconium species, one similar to that of ZrO2 and another with relatively higher electron density were noticed from the Zr 3d core level XPS of Zr- containing catalysts. The valence band (VB) XPS studies revealed that for Zr-containing catalysts, the Cu 3d anti-bonding orbital splits from the main VB and shifts toward lower binding energy (BE). The surface Cu/(Al + Zr) ratios were found to be close to those in the bulk while segregation of Zn at the surface was evidenced in all samples. The XANES and EXAFS results also indicated the existence of CuO and ZnO-like species, whose local environments are modified with respect to the chemical composition. The EXAFS study of the Zr-containing catalysts indicated the existence of a “Cu–O–Zr” bonding with a Cu–Zr distance in the range 3.5 to 3.9 A. The results indicated the existence of a Cu–Zr synergistic interaction in these catalysts which improved the catalytic performance in the OSRM reaction

Characterization of Rh−Cr Mixed-Oxide Nanoparticles Dispersed on (Ga1-xZnx)(N1-xOx) as a Cocatalyst for Visible-Light-Driven Overall Water Splitting

Abstract: The structure of Rh−Cr mixed-oxide (Rh2-yCryO3) nanoparticles dispersed on (Ga1-xZnx)(N1-xOx) is characterized by electron microscopy and X-ray spectroscopy. The Rh2-yCryO3 nanoparticle is an efficient cocatalyst for photocatalytic overall water splitting on the (Ga1-xZnx)(N1-xOx) solid solution and is loaded onto the catalyst by impregnation from an aqueous solution containing Na3RhCl6·2H2O and Cr(NO3)3·9H2O followed by calcination in air. Impregnation of the (Ga1-xZnx)(N1-xOx) with 1 wt % Rh and 1.5 wt % Cr followed by calcination at 623 K for 1 h provides the highest photocatalytic activity. Structural analyses reveal that the activity of this photocatalyst is strongly dependent on the generation of trivalent Rh−Cr mixed-oxide nanoparticles with optimal composition and distribution.